Heretofore, aircraft, whether military or civilian, have been equipped with various sorts of communication or radar array antennas.
In an array antenna of the type referred to, a plurality of antenna elements are mounted on a base in a side-by-side positional relationship and the antenna is usually mounted on the outside surface of an airplane body (wall body).
Further, an array antenna installed on the outside, for which a high environmental resistance performance is demanded, employs in many cases a structure wherein the aforementioned antenna elements are enclosed by a radome.
FIG. 8 exemplifies a microstrip array antenna as described, which comprises a metallic base 1, a grounding plate 2, a dielectric substrate 3, a radiation conductor 4 (antenna element), a coaxial cable 10 (power supply means) which is fixed in the metallic base 1 and the grounding plate 2 as passed therethrough to supply power from the cable via a central conductor 10a to the radiation conductor 4, these members being sequentially stacked on the metallic base 1 in this order.
Fixed on the metallic base 1 by means of rivets 8 at its peripheral edge is a radome 6 so that a metallic spacer 7 disposed between the radome and the radiation conductor 4 maintains a predetermined gap 5.
In the prior art array antenna, however, not only external parts including the metallic base 1, the radome 6 and so on but also internal constituent parts are all formed in a planar configuration. For this reason, in order for the prior art array antenna to be fixedly mounted on such a curved surface as the outside surface of an airplane, a spacer 12 must be provided between the bottom surface of the metallic base 1 and an airplane body 11 and as shown in FIG. 9.
Such provision of the spacer, however, causes an increase of a projection h of the array antenna from the airplane body at its both ends, which results in that the air resistance of the antenna is increased and thus this involves the vibration and deformation of the radome 6 due to the air pressure.
Since the radome 6 is usually made of such dielectric material as resin, a deformation in the radome 6 positioned in a beam radiation path causes a variation in the total dielectric constant of the radiation conductor 4 above it, which affects the beam characteristics of the antenna.
Further, the repetitive deformation of the radome 6 has a great effect on the mechanical strength of the radome 6 itself.
Meanwhile, this sort of array antenna to be externally installed includes a connector which passes through the airplane body to connect the respective antenna elements and a transmitter/receiver.
This is realized in the prior art, by positioning a flange part 24 of a connector 23 on an outer surface of an airplane body 25 and tightening the flange part 24 to the airplane body 25 through a packing 26 to thereby maintain the interior of the airplane body 25 in an air-tight condition, as shown in FIG. 10.
In the event where it is necessary to supply power individually to a multiplicity of antenna elements as in a phased array antenna, however, the above technique requires the formation of a multiplicity of holes in a relative small zone on the airplane body 25, thus making it difficult to secure the strength of this zone and the air tightness of the airplane body and further involving a large number of hole formation steps.
And this technique, when it is desired to make such holes in the body of an existing airplane being used, involves more difficulties in attaining that purpose.
In view of the above circumstances, it is an object of the present invention to provide an array antenna which can maintain the strength of a casing on which the antenna is to be installed and also maintain the air-tightness of the casing.